1. Field of the Invention
The invention relates to partially embedding through impregnation a non-woven fiber mat to a reinforcing fiber by fully impregnating the reinforcing fiber with thermoplastic and partially impregnating the non-woven fabric mat, thereby leaving exposed at least part of the surface of the non-woven mat for mechanical bonding.
2. Description of Related Art
Bonding to thermoplastic materials is currently accomplished by a variety of surface treatments that chemically modify the surface of the material, including chemical treatments of primers, flame treating or corona treating.
Two problems arise from using these methods. First, the process requires a second processing step that involves additional equipment and cost. Second, the bond is a chemical bond that occurs only at the surface of the interface with two materials.
The prior art bonds a non-woven fiber mat or fabric to the surface of materials, such as steel or aluminum, using a variety of adhesives. The exposed fibers of the non-woven mat or fabric are then available for subsequent bonding.
It is an object of this invention to provide a process for the mechanical attachment of a non-woven fiber mat onto the surface of a thermoplastic sheet to provide a means for the subsequent bonding of the thermoplastic sheet to a variety of materials using a variety of different processes.
To overcome or reduce these problems, the inventors have developed a process for partially embedding a non-woven fiber mat to the surface of a thermoplastic resin impregnated reinforcing fiber sheet.
In one embodiment of the invention, a composite sheet is comprised of:
a) a base layer of reinforcing fibers impregnated with a thermoplastic resin;
b) a mat adjacent to the layer wherein the mat is made of a non-woven fiber;
c) wherein the non-woven fiber mat is partially impregnated with the thermoplastic resin of the base layer thereby creating a mechanical bond between the base layer and the mat to provide a bondable surface with the non-impregnated surface of the non-woven fiber; and
d) wherein the thermoplastic has a melting point less than the melting point of the reinforcing fibers in the base layer and less than the melting point of the non-woven fiber mat.
Another embodiment of the invention is directed toward a method for partially embedding a non-woven fiber mat to a base layer of reinforcing fibers using thermoplastic resin to form a composite sheet having a bondable surface, wherein the method comprises the steps of:
a) providing an impregnated base layer having reinforcing fibers with thermoplastic resin impregnated therein; and
b) partially impregnating the non-woven fiber mat with the thermoplastic resin thereby mechanically bonding one side of the non-woven fiber mat to the thermoplastic resin impregnated within the base layer and forming a composite sheet having a mechanically bondable surface on the other side of the non-woven fiber mat, wherein the thermoplastic resin has a melting point of less than the melting point of the reinforcing fibers in the base layer and less than the melting point of the non-woven fiber mat.
The impregnated base layer may utilize a preexisting impregnated base layer with thermoplastic resin impregnated therein.
The impregnated base layer may be formed by heating a non-consolidated thermoplastic resin and compressing the thermoplastic resin against the reinforcing fibers of the base layer.
Also, the formation of the impregnated base layer and the step of partially impregnating the woven fiber mat may occur simultaneously.
Yet another embodiment is directed to a composite sheet having at least one side with a mechanically bondable face. The composite sheet is produced by a method comprising the steps of:
a) providing a base layer of reinforcing fiber impregnated with a thermoplastic resin and
b) partially impregnating a non-woven fiber of mat with the thermoplastic resin from the impregnated base layer thereby mechanically bonding one side of the non-woven fiber to the woven fiber and forming a composite sheet having a mechanically bondable surface on the other side of the non-woven fiber.